1. Field of the Invention
The present invention generally relates to a quantum well and, more particularly, to a homo-material heterophased quantum well.
2. Description of the Related Art
Gallium Nitride (GaN) has been widely used in producing light-emitting elements due to its broad energy gap, such as light-emitting diodes (LEDs) and laser diodes (LDs). Among various technologies, quantum well technology can improve the light-emitting efficiency of LEDs and LDs. In addition, the quality of quantum well is highly related to the quantum efficiency of the light-emitting elements. Conventional III-nitride quantum well is formed by heterostructures with different energy gaps, such as “GaN/InGaN/GaN”. However, the lighting-emitting efficiency of the light-emitting elements could be degraded by lattice mismatch between the heterostructures. Furthermore, due to the strain resulted from the lattice mismatch, electrostatic field generated by the piezoelectric effect of the conventional quantum well will cause some portion of the energy gap of the quantum well to bend. As a result, the quantum efficiency is directly impacted.
To solve the problem of lattice mismatch, Taiwanese Patent Publication Number 200840082 discloses an LED structure produced with zinc oxide (ZnO). The patent epitaxially grows a ZnO buffer layer and a GaN seed layer on a Lithium Aluminum Oxide (LiAlO2) substrate in sequence. Based on the Wurtzite structure similarity between the ZnO and GaN, high quality GaN may be obtained. With the GaN/ZnO/LiAlO2 structure, multiple quantum wells and a first metallic electrode layer are grown. Then, the LiAlO2 substrate and the ZnO buffer layer are removed by way of etching, and a second metallic electrode layer is further grown under the GaN seed layer. Based on this, not only can the single crystal thin film ZnO buffer be used to successfully grow the GaN seed layer on the LiAlO2 substrate, but it can also reduce the defect density of the GaN for nearly lattice match.
In the LED structure produced with ZnO above, the ZnO and GaN can be combined together to reduce the defect density of the GaN due to their similar Wurtzite structures. However, since heterostructures do not have complete matched lattices due to their mismatched atom size and gap, the quantum well formed by the heterostructures cannot provide an improved light-emitting efficiency for the light-emitting elements. Furthermore, since the piezoelectric effect resulting from the lattice mismatch causes some portion of the energy gap of the quantum well to bend, the quantum efficiency of the light-emitting elements is impacted. Therefore, it is desired to overcome the problems by providing a quantum well formed by homo-materials.